Mycobacterium avium complex (MAC), also known as Macobacterium avium intracellulaire (MAI), is one of the most common systemic gram-positive bacterial infections in patients with AIDS (Armstrong, Young, 1986). MAC infection in humans is associated with infeCtions of the lungs, lymph nodes, skin, bones, soft, tissue, and urinary tract (Chapman, Falk). Current treatment of M. avium complex infection in AIDS patients consists of a variety of drug therapies which generally include ansamysin, clofazamine, isoniazid, and amikacin (Hawkins, Kiehn, Zimmer, Young, 1987, 1988, Baron, Bermudez). Typically the drug amikacin is administered intravenously (I.V.) in free-drug form 2-3 times a day until the level of infection is reduced. The patient is then maintained on a lower-dose regimen to keep the infection in check. One of the difficulties in treating the disease, and one reason that combinations of drugs are now used, is that the infection is active both in the bloodstream, where it is susceptible to certain drugs and in macrophages of the liver, spleen and other reticuloendothelial tissue, where the bacteria is protected from the drugs. That is, current therapy is at best only partially effective in the treatment MAC infection.
Among the aminoglycosides, amikacin has been used for treating MAC infection due to its relatively low minimum inhibitory concentration, particularly in the case of certain MAC serotypes. For example, the minimum inhibitory concentration (MIC) of amikacin against MAC 101 serotype 1 is between 2-4 .mu.g/ml, versus at 36 .mu.g/ml for gentamicin (Bermudez, L.E.M., et al unpublished data); although it is noted that amikacin and gentamicin have comparable MICs against a serotype 4 strain of MAC of between about 16-32 .mu.g/ml (Yajko). Gentamicin would therefore not be expected to be effective in vivo since the toxic level of gentamicin is about 12 .mu.g/ml in the blood, and therefore it is not possible to maintain patients at the inhibitory dose for sustained therapeutic periods. It would be desirable to treat M. avium infection in humans with gentamicin, however, because of the relatively low cost of the drug. It would also be desirable to provide, for treating MAC infection both is immune-compromised patients, a therapeutic method which requires less frequent I.V. dosing and is effective against MAC infection in the bloodstream and reticuloendothelial (RES) tissues.